For example, a CAN protocol is widely used as a communication protocol for LAN or others, and more particularly, a communication protocol for a motor-vehicle communication network.
In this CAN protocol, for example, when a receiver unit provided in an ECU (Electric Control Unit) or others normally receives a message, a response signal with 1 bit, which is called ACK, is transmitted from the corresponding receiver unit to a transmitter unit.
And, by receiving the ACK, the transmitter unit confirms that at least one or more units (ECUs) normally could have received the message.
As the communication technique with the LAN communication protocol of this type, a technique capable of achieving high-speed printing of a printer is known, in which, by providing an ACKX width variable circuit for changing an ACKX signal width and an ACKX width set key for setting an ACKX signal width related to the change in this ACKX width variable circuit, a data transfer speed from a host computer to the printer is improved as high as possible in accordance with performances of the host computer and the printer (see Patent Document 1).